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1.
Studies of impurity levels in Rh-doped and Ce-doped photorefractive BaTiO3   总被引:1,自引:0,他引:1  
Impurity levels, light-induced and thermo-induced charge transfer processes in Rh-doped and Ce-doped photorefractive BaTiO3 were studied. The thermal depths and optical transitions of these impurity levels in the crystals were determined by using such methods as light-induced absorption, thermo-induced absorption, and grating dark decay. The origins of these impurity levels were discussed. We demonstrated, for the first time to our knowledge, that thermo-induced absorption spectroscopy is a useful and complementary technique for investigating the impurity levels in photorefractive crystals. With this technique, the deep impurity level generated by Ce in BaTiO3:Ce was revealed and identified. Received: 7 July 1999 / Revised version: 24 September 19999 / Published online: 2 February 2000  相似文献   

2.
We apply, for the first time to our knowledge, photorefractive grating spectroscopy to obtain not-yet-known data on the anisotropy of the dielectric permittivity of Sn2P2S6. Two independent techniques are used, one based on measurements of the amplitude of the space-charge field grating as a function of grating spacing and the other based on measurements of the grating decay time, also as a function of grating spacing. Both techniques provide close values for the anisotropy, which appears to be well pronounced, a ratio εxxzz≈4 is revealed for two of the three independent components of the dielectric tensor. Our data also allow us to conclude that the charge mobility is nearly isotropic in the same plane, μxxzz≈1. Received: 2 December 2002 / Published online: 26 March 2003 RID="*" ID="*"Corresponding author. Fax: +380-44/265-2359, E-mail: odoulov@iop.kiev.ua  相似文献   

3.
We demonstrate an optical processor based on spectral hole burning (SHB) that maps the carrier frequency into the time domain and the pulse repetition frequency (PRF) into the spatial domain by illuminating an SHB crystal with a signal beam that is scanned by a tilting mirror across a slice of the crystal. This time-to-space mapping makes it possible to measure signal envelopes with a resolution of . A signal with a pulsed envelope engraves a vertical absorption grating with a spatial periodicity given by the product of the PRF and the scan velocity. Reading the grating, which the crystal stores for up to T1, with a collimated beam yields orders diffracted at angles proportional to the PRF, which are Fourier-transformed to produce spots displaced from the DC position by distances proportional to the PRF. Increasing the PRF increases the grating periodicity, causing the diffracted spots to move away from the DC position.  相似文献   

4.
Total absorption of O2 induced by collisions with N2 has been measured at room temperature in the Herzberg continuum using a one meter normal incidence grating monochromator. The enhanced absorption is ascribed to the formation of O2-O2 and O2-N2 dimers. The interaction constants for these dimers are determined and utilized to investigate their effect on the absorption of solar radiation in the stratosphere.  相似文献   

5.
用泵浦探测技术研究了掺杂CeO2的75TeO2-25Nb2O5-5ZnO玻璃在飞秒激光诱导的瞬态光栅多级自衍射。从拉曼和吸收光谱中研究了玻璃的结构特性,并证明了此玻璃中存在Ce3+离子。这种瞬态光栅起因于光克尔效应,并通过Ce3+离子中1S0?1F3电子能级跃迁形成的激发态粒子数光栅而改善,一级衍射信号的转换效率可达到11%。这些实验结果显示了掺杂CeO2的75TeO2-25Nb2O5-5ZnO飞玻璃在全转换开关中具有广泛应用。  相似文献   

6.
Using a one meter normal incidence grating monochromator, the total absorption of radiation for O2 has been reinvestigated between 2000–2500 Å. The absorption cross sections of O2 and O4 are then derived from total absorption measurements and compared with other available data. Additional measurements of O2 absorption have been made in the presence of Ar which does not absorb in this spectral region and is chemically inactive with O2. It is found that the absorption of oxygen increases in the presence of Ar, which is interpreted as due to the formation of O2-Ar dimers. The significance of these measurements is discussed.  相似文献   

7.
Laser-induced thermal gratings (LITG) were generated in mixtures of ethylene and ammonia in nitrogen using mid-infrared laser radiation from a grating-tuned, low-pressure, pulsed (5 ms pulse width) CO2 laser, and read out with a continuous wave Nd:YLF laser. The LITG signal intensity was measured as a function of pressure (0.1–2 MPa) and temperature (300–800 K, at 0.1 and 1 MPa) by tuning the laser to the accidental coincidences of the 10P(14) and 10R(6) emission lines with molecular absorption transitions of C2H4 and NH3, respectively. Comparisons are made with theoretical predictions for the grating efficiency from a simple thermalization model. A theoretical comparison of the temporal LITG signal response for three excitation pulse shapes – a delta function, a realistic pulse, and a square wave is presented. Furthermore, it is shown that for NH3, most of the decrease of the LITG signal intensity with increasing temperature is due to the corresponding decrease in fractional molecular absorption of the pump beam radiation. The diagnostic capabilities of the mid-infrared LITG experiment is demonstrated for spatially resolved ethylene measurements with long laser pulses in a premixed stoichiometric CH4–air flame at atmospheric pressure. Received: 17 March 2000 / Revised version: 23 March 2000 / Published online: 13 September 2000  相似文献   

8.
We present a two-dimensional model to account for the role of heat-conducting walls in the measurement of heat transport and Soret-effect-driven mass transport in transient holographic grating experiments. Heat diffusion into the walls leads to non-exponential decay of the temperature grating. Under certain experimental conditions it can be approximated by an exponential function and assigned an apparent thermal diffusivity Dth, app < Dth, s, where Dth,s is the true thermal diffusivity of the sample. The ratio Dth, app/Dth, s depends on only three dimensionless parameters, d /ls, κsw, and Dth, s/Dth, w. d is the grating period, ls the sample thickness, κs and κw the thermal conductivities of sample and wall, respectively, and Dth,w the thermal diffusivity of the wall. If at least two measurements are performed at different d /ls, both Dth,s and κs can be determined. Instead of costly solving PDEs, Dth,s can be obtained by finding the zero of an analytic function. For thin samples and large grating periods, heat conduction into the walls plays a predominant role and the concentration grating in binary mixtures is no longer one-dimensional. Nevertheless, the normalized heterodyne diffraction efficiency of the concentration grating remains unaffected and the true thermal and collective diffusion coefficient and the correct Soret coefficient are still obtained from a simple one-dimensional model.  相似文献   

9.
A dye laser system allowing simultaneous tunable two-wavelength oscillationin the ultraviolet has been developed. An intra-cavity dual beam system employs one diffraction and grating frequencydoubling at both wavelengths is achieved with bidirectional illumination of a single KDP crystal. The system characteristics will be discussed with respect to application in a differential absorption lidar operating around 300 nm for atmospheric SO2 detection.  相似文献   

10.
We report the direct recording of electron-based photorefractive hologram in nominally undoped Bi12TiO20 crystals using 780 nm wavelength light without pre-exposure or any kind of previous processing. A lower intensity absorption grating is also detected. Pre-exposure with shorter wavelength produces an extended lifetime hole-based complementary grating on another photoactive center level and leads to enhanced recording.PACS 42.70.Nq; 42.70.Ln; 42.70.Gi; 42.65.Hw  相似文献   

11.
A pulsed optical parametric oscillator (OPO) operated in an optical cavity with a grazing-incidence grating configuration (GIOPO) was used for sensitive photoacoustic detection of trace quantities of dinitrogen oxide (N2O). The (ν13) combination vibration band of N2O was excited with the idler beam of the GIOPO at 2.86 μm using an optical cavity optimized for the idler beam. The linewidth of the GIOPO could be reduced to 0.4 cm-1, allowing the rotational structure of the absorption spectrum to be resolved. A concentration sensitivity (signal-to-noise ratio=3) of 60 parts in 109 by volume (60 ppb V) N2O in synthetic air was obtained. This may be sufficient for continuous monitoring of N2O in the atmosphere. Received: 29 April 2002 / Revised version: 4 June 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +49-6221/54-4255, E-mail: peter.hess@urz.uni-heidelberg.de  相似文献   

12.
We demonstrate an extension of forming a photorefractive volume grating in an Fe:LiNbO3 crystal by chirped intense femtosecond laser pulses generated from a Ti:Al2O3 regenerative amplifier at 1 kHz. We confirm that one-photon absorption is still dominant in the Fe:LiNbO3 crystal up to 70 GW/cm2. To generate a photorefractive grating at such a low laser repetition rate within a practical writing time, the laser pulse intensity is increased to >30 GW/cm2. Furthermore, we demonstrate the amplification of femtosecond laser pulses by the chirped volume grating that is written in the Fe:LiNbO3 by two-wave mixing.  相似文献   

13.
Downstream mass spectrometry is successfully used in the reactive ion-beam etching of dielectric diffraction gratings of deep grooves with vertical sidewalls to achieve in situ endpoint detection. Silica (SiO2) gratings with a Sc2O3 etch-stop layer are fabricated by reactive ion-beam etching with CHF3 as etchant, and the mass spectrometric signal of SiF3+ produced by the reactive etching of the SiO2 grating material is monitored. When the etch-stop layer is reached, a drop of this signal occurs. By comparing the monitoring curves and resulting gratings of different etching methods, we find that the decrease of the monitored signal is strongly influenced by the sidewall steepness of the etched grating grooves. All conditions being equal, the greater sidewall steepness renders the faster decrease of the signal. Consequently, the proposed approach of endpoint detection applies well to the gratings with steep sidewalls. With the help of two previously developed methods, the sidewall steepness of grating grooves is increased, and the optimal endpoint is detected. Employing the proposed technique, we have reproducibly fabricated dielectric gratings with proper groove depth and even groove bottom.  相似文献   

14.
We fabricated and measured the far-field optical properties of a sub-wavelength Si3N4 (silicon nitride) two dimensional grating. Frequency-dependent transmission measurements from a white-light source revealed that both transverse magnetic (TM) and transverse electric (TE) modes were excited on the grating. We determined the dispersion relations of the modes by tilting the sample with respect to the incoming light beam and measuring the frequency shift of the absorption features. By comparing to a simple model, we determined the effective refractive index for the TM and TE modes and the geometrical constants for the grating. This information enables gratings with desired optical properties to be designed and fabricated. The application of the sub-wavelength grating for surface-enhanced Raman scattering (SERS) is demonstrated.  相似文献   

15.
An inductively coupled plasma etching process to fabricate notched long-period fiber gratings for CO2 gas sensing is proposed in this article. In the gas sensing test, the 15% mixed CO2 gas was used for characterization of CO2 adsorption by the amine-modified nanoporous silica foams of the notched long-period fiber grating sensor. The results shows the spectra were changed with the CO2 gas flow within 13 min. During the absorption process, the transmission of the resonant dip was decreased by 2.884?dB. Therefore, the proposed notched long-period fiber grating gas sensor shows good performance and is suitable as a gas sensor for monitoring the CO2 adsorption process.  相似文献   

16.
A combined Raman elastic-backscatter lidar has been developed. A XeCl excimer laser is used as the radiation source. Inelastic Raman backscatter signals are spectrally separated from the elastic signal with a filter or grating polychromator. Raman channels can be chosen to register signals from CO2, O2, N2, and H2O. Algorithms for the calculation of the water-vapor mixing ratio from the Raman signals and the particle extinction and backscatter coefficients from both elastic and inelastic backscatter signals are given. Nighttime measurements of the vertical humidity distribution up to the tropopause and of particle extinction, backscatter, and lidar ratio profiles in the boundary layer, in high-altitude water and ice clouds, and in the stratospheric aerosol layer are presented. Daytime boundary-layer measurements of moisture and particle extinction are made possible by the improved daylight suppression of the grating polychromator. Test measurements of the CO2 mixing ratio indicate the problems for the Raman lidar technique in monitoring other trace gases than water vapor.  相似文献   

17.
In a photorefractive Bi12SiO20 crystal with high applied electric ac field of square-wave shape a fast two-wave coupling response (less than 1 s) and a slow hologram readout decay (minutes) was found for a wavelength of 633 nm. This can be explained by electron–hole transport with two trap levels. An intensity dependence of the slower complementary grating was found. Illuminating with the readout wave without applied electric field leads to a very slow grating decay (many hours). Received: 18 November 1998 / Revised version: 3 February 1999 / Published online: 7 April 1999  相似文献   

18.
During holographic recording in lead germanate (Pb5Ge3O11) crystals two types of refractive-index gratings are observed. One has a very fast response whereas the second builds up comparably slowly. Measurements of diffraction efficiency and two-beam coupling are carried out to study the formation of both gratings and to obtain the relative phase between them. Differently doped and thermally treated samples are divided into four classes due to their different time evolution of diffraction efficiency and of the energy transfer direction during two-beam coupling. The classification depends on doping and treatment. For Ni-doped and thermally treated samples dark and photo conductivities corresponding to the slow grating are determined, indicating that Ni-doping combined with oxidation enhances the properties of the slow grating. Received: 18 November 1998 / Published online: 7 April 1999  相似文献   

19.
Precise patterning by laser ablation requires sufficient absorption. For weak absorbers like fused silica indirect methods using external absorbers have been developed. A novel approach using a solid SiO absorber coating is described. Irradiation by an ArF excimer laser (wavelength 193 nm) is leading to ablation of the coating and, at sufficiently high fluence, of the fused silica substrate. The remaining coating in the unexposed areas is removed afterwards by large area irradiation. The fluence threshold for substrate ablation using a 28 nm thick absorber layer is about 1.1 J/cm2. Single pulse ablation rates of up to 800 nm and a surface roughness of R a<5 nm are obtained. High resolution grating patterns with 400 nm period and a modulation depth of 80 nm are possible. The process can be described as controlled plasma mediated ablation.  相似文献   

20.
The effect of temperature on the total absorption of O2 induced by collisions with N2 has been measured at various temperatures in the Herzberg continuum using a one meter normal incidence grating monochromator. It is observed that absorption increases as the temperature decreases which is ascribed to changes in the rate of formation of the dimers O2-O2 and O2-N2. The interaction constants for these dimers are determined as functions of temperature and are then utilized to calculate the heat of dissociations of O2-O2 and O2-N2. Their respective values are found to be 0.0146±0.001 and 0.0425±0.002 eV. Also, the interaction constants for these dimers measured at 200±1°K are utilized to investigate their effect on the absorption of solar radiation in the stratosphere.  相似文献   

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